The present invention relates, in general, to ultrasonic systems and, in particular, to methods and circuitry for driving a high-power ultrasonic transducer for use with a varying load.
Ultrasound technology is utilized in a variety of applications from machining and cleaning of jewelry, performing surgical operations to the processing of fluids, including hydrocarbons. The basic concept of ultrasonic systems involves the conversion of high frequency electric energy into ultrasonic frequency mechanical vibrations using transducer elements. Such systems typically include a driver circuit that generates electrical signals which excite a piezoelectric (or magnetostrictive) transducer assembly. A transmission element such as a probe connects to the transducer assembly and is used to deliver mechanical energy to the target.
Ultrasonic transducers include industrial and medical resonators. Industrial resonators deliver high energy density in order to substantially affect the materials with which they are in contact. Common uses of industrial resonators include welding of plastics and nonferrous metals, cleaning, abrasive machining of hard materials, cutting, enhancement of chemical reactions (sonochemistry), liquid processing, defoaming, and atomization. Usual frequencies for such operations are between 15 kHz and 40 kHz, although frequencies can range as low as 10 kHz and as high as 100+ kHz. Medical resonators include devices for cutting, disintegrating, cauterizing, scraping, cavitating, dental descaling, etc.
A transducer assembly for an industrial ultrasonic application may be referred to as an industrial ultrasonic stack, and may include a probe (or a sonotrode, or a horn), a booster, and a transducer (or a converter). The probe contacts the load and delivers power to the load. The probe's shape depends on the shape of the load and the required gain. Probes are typically made of titanium, aluminum, and steel. The booster adjusts the vibrational output from the transducer and transfers the ultrasonic energy to the probe. The booster also generally provides a method for mounting the ultrasonic stack to a support structure. The active elements are usually piezoelectric ceramics although magnetostrictive materials are also used.
Existing technology for driving ultrasonic probes has been developed for driving a system at one desired frequency and power level for a specific process. This known technology utilizes an electrical system based on a Silicon Controlled Rectifier (SCR). Typically, SCR's require a forced turn off system having a particular capacitor value to control and turn off the SCR which in turn limits the operating frequency of the electrical system. Also, the SCR systems are limited to much lower power levels which do not allow for the effective control of an ultrasonic probe at higher power levels. As used herein, a high power level refers to power levels of at least 500 Watts. For example, the SCR-based ultrasonic generators drive ultrasonic probes which are designed for a specific load such as molten steel. However, an SCR-based ultrasonic generator when used in a process which exposes an attached ultrasonic probe to varying load conditions, such as the processing of liquid hydrocarbons, limits the effectiveness of the probe in different liquids. This limited effectiveness is due to the loading effect different liquids will have on the ultrasonic probe. In addition, even for a given liquid, density and phase change effects can vary the loading on the ultrasonic probe.
There is therefore a need for a high-power and variable load driving circuit for an ultrasonic generator that does not suffer from the shortcomings of SCR-based ultrasonic generators.